U.S. patent application number 15/770447 was filed with the patent office on 2018-11-01 for controller for a motor vehicle and method.
The applicant listed for this patent is Jaguar Land Rover Limited. Invention is credited to Matthew HANCOCK, Steve LIGGINS, Simon MESSAGE.
Application Number | 20180312081 15/770447 |
Document ID | / |
Family ID | 55133371 |
Filed Date | 2018-11-01 |
United States Patent
Application |
20180312081 |
Kind Code |
A1 |
HANCOCK; Matthew ; et
al. |
November 1, 2018 |
CONTROLLER FOR A MOTOR VEHICLE AND METHOD
Abstract
A controller for a motor vehicle powertrain, the controller
being configured to control the amount of torque generated by each
of a plurality of drive torque sources, each drive torque source
being coupled via a respective torque transfer arrangement to a
respective group of one or more wheels, the controller being
configured to cause a first of the drive torque sources, during
acceleration, deceleration and substantially constant speed
operation, substantially continually to apply a drive torque to a
first group of one or more wheels to which the first drive torque
source is coupled acting in a first direction relative to a
longitudinal axis of the vehicle and causes a second of the drive
torque sources, during acceleration, deceleration and substantially
constant speed operation, substantially continually to apply a
drive torque to a second group of one or more wheels to which the
second drive torque source is coupled, the direction of drive
torque applied to the second group being in a second direction
opposite the first such that a net drive torque applied to the
first and second group in combination corresponds substantially to
a predetermined drive torque demand value, the predetermined torque
demand value being determined at least in part by reference to a
torque demand signal received by the controller.
Inventors: |
HANCOCK; Matthew; (Whitley,
Coventry, GB) ; LIGGINS; Steve; (Whitley, Coventry,
GB) ; MESSAGE; Simon; (Whitley, Coventry,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jaguar Land Rover Limited |
Whitley, Coventry, Warwickshire |
|
GB |
|
|
Family ID: |
55133371 |
Appl. No.: |
15/770447 |
Filed: |
October 26, 2016 |
PCT Filed: |
October 26, 2016 |
PCT NO: |
PCT/EP2016/075772 |
371 Date: |
April 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60L 15/2063 20130101;
B60W 20/14 20160101; Y02T 10/62 20130101; Y02T 10/72 20130101; B60W
10/06 20130101; B60W 10/08 20130101; B60W 30/18127 20130101; B60Y
2200/91 20130101; B60L 15/20 20130101; B60K 6/52 20130101; B60W
10/26 20130101; B60W 30/18109 20130101; B60L 15/2072 20130101; B60W
30/02 20130101; B60W 2710/083 20130101; B60L 15/10 20130101; B60L
15/32 20130101; B60W 2720/403 20130101; B60W 2720/406 20130101;
B60W 20/13 20160101; B60L 2240/423 20130101; B60W 20/17
20160101 |
International
Class: |
B60L 15/32 20060101
B60L015/32; B60W 10/08 20060101 B60W010/08; B60W 20/17 20060101
B60W020/17 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 2015 |
GB |
1520818.4 |
Claims
1. A controller for a motor vehicle powertrain, wherein the
controller is configured to control an amount of torque generated
by each of a plurality of drive torque sources, each of the
plurality of drive torque sources being coupled via a respective
torque transfer arrangement to a respective group of one or more
wheels, wherein the controller is configured to cause a first one
of the plurality of drive torque sources, during acceleration,
deceleration and substantially constant speed operation,
substantially continually to apply a drive torque to a first group
of the one or more wheels to which the first one of the plurality
of drive torque sources is coupled acting in a first direction
relative to a longitudinal axis of the vehicle, and to cause a
second one of the plurality of drive torque sources, during
acceleration, deceleration and substantially constant speed
operation, substantially continually to apply a drive torque to a
second group of the one or more wheels to which the second one of
the plurality of drive torque sources is coupled, the direction of
drive torque applied to the second group of the one or more wheels
being in a second direction opposite the first direction such that
a net drive torque applied to the first and second groups of the
one or more wheels in combination corresponds substantially to a
predetermined drive torque demand value, wherein the controller is
configured to determine the predetermined torque demand value at
least in part by reference to a torque demand signal received by
the controller.
2. The controller according to claim 1, wherein the first group of
the one or more wheels correspond to a pair of front wheels of the
vehicle, and wherein the second group of the one or more wheels
correspond to a pair of rear wheels of the vehicle.
3. The controller according to claim 1, wherein the controller is
further configured to control the first and second ones of the
plurality of drive torque sources, wherein each of the first and
second ones of the plurality of drive torque sources comprises at
least one electric machine.
4. The controller according to claim 3, wherein the first direction
is a rearward direction relative to a front of the vehicle and the
second direction is a forward direction relative to the front of
the vehicle, wherein when the vehicle is moving in the forward
direction the controller causes the first one of the plurality of
drive torque sources to operate as a generator to generate
electrical current to recharge an electrical charge storage
device.
5. The controller according to claim 1, wherein the controller is
further configured to receive a brake signal indicative of brake
force demand from at least one of a drive brake control device and
a speed control system.
6. The controller according to claim 5, 4 wherein the controller is
further configured, when the vehicle is moving in a forward
direction, to cause the first one of the plurality of drive torque
sources to provide an increased amount of torque in the first
direction in response to receipt by the controller of the brake
signal.
7. The controller according to claim 5, wherein the controller is
further configured, when the vehicle is moving in a rearward
direction, to cause the second one of the plurality of drive torque
sources to provide an increased amount of torque in the first
direction in response to receipt by the controller of the brake
signal.
8. The controller according to claim 4, wherein the controller is
further configured, when the vehicle is moving in the rearward
direction, to cause the second one of the plurality of drive torque
sources to apply negative drive torque, wherein the negative drive
torque is drive torque acting in a direction opposite the rearward
direction of travel, by causing the first one of the plurality of
drive torque sources to operate as the generator to generate
electrical current to recharge the electrical charge storage
device.
9. The controller according to claim 1, comprising an electronic
processor having an electrical input for receiving the torque
demand signal, and an electronic memory device electrically coupled
to the electronic processor and having instructions stored therein,
wherein controller is further configured to access the memory
device and execute the instructions stored therein.
10. A vehicle comprising a body, a plurality of wheels, a
powertrain to drive the plurality of wheels, a braking system to
brake the plurality of wheels, and the controller according to
claim 1.
11. A method of controlling a motor vehicle powertrain, the method
comprising: controlling an amount of torque generated by each of a
plurality of drive torque sources, each of the plurality of drive
torque sources being coupled via a respective torque transfer
arrangement to a respective group of one or more wheels; causing a
first one of the plurality of drive torque sources, during
acceleration, deceleration and substantially constant speed
operation, substantially continually to apply a drive torque to a
first group of the one or more wheels to which the first one of the
plurality of drive torque sources is coupled acting in a first
direction relative to a longitudinal axis of the vehicles and
causing a second one of the plurality of drive torque sources,
during acceleration, deceleration and substantially constant speed
operation, substantially continually to apply a drive torque to a
second group of the one or more wheels to which the second one of
the plurality of drive torque sources is coupled, the direction of
drive torque applied to the second group of the one or more wheels
being in a second direction opposite the first direction such that
a net drive torque applied to the first and second groups of the
one or more wheels in combination corresponds substantially to a
predetermined drive torque demand value, the predetermined torque
demand value being determined at least in part by reference to a
torque demand signal.
12. A computer program product comprising a non-transitory computer
readable carrier medium having encoded thereon instructions that,
when executed on a processor, cause the processor to perform the
method of claim 11.
13-16. (canceled)
17. The controller according to claim 1, wherein the controller is
further configured, when the vehicle is substantially stationary,
to cause the first one of the plurality of drive torque sources to
develop drive torque in the first direction, and to cause the
second one of the plurality of drive torque sources to develop
drive torque in the second direction.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a controller for a motor
vehicle and method. Aspects of the invention relate to a controller
and a method.
BACKGROUND
[0002] It is known to provide an electrically driven vehicle
whereby a battery provides electrical power through an inverter to
a drive motor. The drive motor is generally connected to two wheels
of the vehicle through a torque transfer assembly that has a
transmission coupled to a differential gearbox via a drive shaft.
The differential gearbox delivers drive torque to side shafts of
the assembly that in turn deliver torque to each of two wheels of
the vehicle.
[0003] It is a characteristic of torque transfer devices such as
geared transmissions and differential gearboxes that backlash is
present within each gear mesh thereof and also in supporting
bearings. When the direction of torque transmission through the
device reverses the backlash is crossed and this can result in the
generation of an audible noise and/or jerk experienced by the
driver or a passenger. It is to be understood that backlash may be
caused by a combination of free play within gearboxes and the
torsional compliance of driveline components. Backlash occurs for
example when a vehicle transitions from operating in an engine
overrun operating condition, where a driver may for example have
released both an accelerator pedal and a brake pedal of the
vehicle, such that the vehicle is slowly decelerating, to a state
in which the accelerator pedal is depressed and the vehicle is
accelerating. As the powertrain transitions from a state in which
energy is being put into the engine in order to overcome frictional
forces and a state in which the engine is delivering energy to the
powertrain, the driveline transitions from a state of negative
torque to positive torque and NVH in the form of a heavy `thump`
may be heard and felt by occupants of the vehicle.
[0004] In some cases a hybrid vehicle may be capable of providing
drive torque to front wheels of a vehicle from an internal
combustion engine and an electrical drive to rear wheels of the
same vehicle from an electric machine. The hybrid vehicle may be
arranged such that the front and rear wheels are not mechanically
coupled, i.e. there is no prop shaft connecting the respective sets
of wheels.
[0005] The proportion of the total required drive torque that is
provided by each torque source may be controlled in order to
improve the overall efficiency of operation of the vehicle and so
provide improved fuel economy.
[0006] It is recognised that the torque distribution between torque
sources also affects stability of the vehicle. For example,
steering feel and handling balance as experienced by the driver may
be controlled by adjusting the relative torque distribution between
the two sources. For example, if the electric drive system
connected to the rear wheels is operating in an electrical
generation mode, recharging a battery of the vehicle, and the road
surface is relatively slippery, the amount of regeneration torque
developed by the wheels may be limited by a controller of the
powertrain in order to maintain stability of the rear wheels.
[0007] It is an aim of embodiments of the present invention to
reduce noise and/or jerk caused by torque reversal in one or more
components of a vehicle torque transfer assembly.
SUMMARY OF THE INVENTION
[0008] Aspects and embodiments of the invention provide a
controller for a motor vehicle powertrain and a method of
controlling a motor vehicle powertrain.
[0009] In one aspect of the invention for which protection is
sought there is provided a controller for a motor vehicle
powertrain, the controller being configured to control the amount
of torque generated by each of a plurality of drive torque sources,
each drive torque source being coupled via a respective torque
transfer arrangement to a respective group of one or more wheels,
[0010] the controller being configured to cause a first of the
drive torque sources, during acceleration, deceleration and
substantially constant speed operation, substantially continually
to apply a drive torque to a first group of one or more wheels to
which the first drive torque source is coupled acting in a first
direction relative to a longitudinal axis of the vehicle and causes
a second of the drive torque sources, during acceleration,
deceleration and substantially constant speed operation,
substantially continually to apply a drive torque to a second group
of one or more wheels to which the second drive torque source is
coupled, the direction of drive torque applied to the second group
being in a second direction opposite the first such that a net
drive torque applied to the first and second group in combination
corresponds substantially to a predetermined drive torque demand
value, the predetermined torque demand value being determined at
least in part by reference to a torque demand signal received by
the controller.
[0011] It is to be understood that when the vehicle is parked the
controller may be configured to assume a standby or off condition
in which neither of the plurality drive torque sources generate
drive torque.
[0012] It is to be understood that, by maintaining the direction of
application of torque in the same direction relative to a body of
the vehicle, lash crossing associated with transfer of torque from
each of the plurality of drive torque sources to the respective
group of one or more wheels may be substantially prevented. Some
embodiments of the present invention therefore permit a vehicle to
be operated within acceptable powertrain noise, vibration and
harshness (NVH) constraints using powertrain components of reduced
tolerance. For example, in a geared torque transfer arrangement,
the use of components of reduced tolerance may permit a reduction
in cost of the vehicle to be enjoyed. Alternatively or in addition,
a reduction in NVH experienced by vehicle occupants may be enjoyed
for a given set of powertrain components compared with a vehicle
not according to an embodiment of the present invention.
[0013] Embodiments of the present invention may be useful in
vehicles in which both drive torque sources are electric machines.
Some embodiments may be useful in vehicles in which at least one
drive torque source is an electric machine. Some embodiments may be
useful in vehicles in which at least one drive torque source is an
internal combustion engine.
[0014] Optionally, the first group of one or more wheels correspond
to one or more front wheels of the vehicle and the second group of
one or more wheels correspond to one or more rear wheels of the
vehicle.
[0015] The controller may be configured to control the first and
second drive torque sources, each comprising at least one electric
machine.
[0016] The controller may be configured wherein the first direction
is a rearward direction relative to a front of the vehicle and the
second direction is a forward direction relative to a front of the
vehicle, wherein when the vehicle is moving in the forward
direction the controller causes the first drive torque source to
operate as a generator to generate electrical current to recharge
an electrical charge storage device.
[0017] Thus, when the vehicle is moving in a forward direction, the
first drive torque source applies negative drive torque being drive
torque acting in a direction opposite the forward direction of
travel by causing the first drive torque source to operate as a
generator to generate electrical current to recharge an electrical
charge storage device.
[0018] It is to be understood that if the first group of one or
more wheels correspond to the front wheels and the second group of
one or more wheels correspond to the rear wheels, a rearward weight
shift associated with acceleration of the vehicle in a forward
direction (corresponding to movement in the second direction)
causes additional pressure to be placed on the one or more rear
wheels of the vehicle, enhancing traction of the wheels causing
acceleration during acceleration, whilst a forward weight shift
associated with braking of the vehicle causes additional pressure
to be placed on the one or more front wheels of the vehicle,
enhancing traction of the wheels causing braking. Similarly, if the
direction of torque application to the first and second groups of
one or more wheels continues to be in the same direction when the
vehicle moves backwards (corresponding to movement in the first
direction), the rearward weight shift (relative to the direction of
travel of the vehicle) associated with acceleration of the vehicle
in the rearward direction causes additional pressure to be placed
on the one or more front (now trailing) wheels of the vehicle,
enhancing traction of the wheels causing acceleration during
acceleration, whilst a forward weight shift (relative to the
direction of travel of the vehicle) associated with braking of the
vehicle causes additional pressure to be placed on the one or more
rear (now leading) wheels of the vehicle, enhancing traction of the
wheels causing braking.
[0019] The controller may be configured to receive a brake signal
indicative of brake force demand from at least one of a drive brake
control device and a speed control system.
[0020] The controller may be configured, when the vehicle is moving
in the forward direction, to cause the first drive torque source to
provide an increased amount of torque in the first direction in
response to receipt by the controller of the brake signal.
[0021] Thus the first drive torque source may cause additional
regenerative brake force in response to a requirement for braking
from a driver and/or a speed control system such as an adaptive (or
active) cruise control system or other speed control system.
[0022] The controller may be configured, when the vehicle is moving
in the rearward direction, to cause the second drive torque source
to provide an increased amount of torque in the first direction in
response to receipt by the controller of the brake signal.
[0023] The controller may be configured, when the vehicle is moving
in the rearward direction, to cause the second drive torque source
to apply negative drive torque being drive torque acting in a
direction opposite the rearward direction of travel by causing the
first drive torque source to operate as a generator to generate
electrical current to recharge the electrical charge storage
device.
[0024] The controller may comprise an electronic processor having
an electrical input for receiving the torque demand signal, and an
electronic memory device electrically coupled to the electronic
processor and having instructions stored therein, [0025] wherein
the controller being configured to cause a first of the drive
torque sources, during acceleration, deceleration and substantially
constant speed operation, substantially continually to apply a
drive torque to a first group of one or more wheels to which the
first drive torque source is coupled acting in a first direction
relative to a longitudinal axis of the vehicle and causes a second
of the drive torque sources, during acceleration, deceleration and
substantially constant speed operation, substantially continually
to apply a drive torque to a second group of one or more wheels to
which the second drive torque source is coupled, the direction of
drive torque applied to the second group being in a second
direction opposite the first such that a net drive torque applied
to the first and second group in combination corresponds
substantially to a predetermined drive torque demand value, the
predetermined torque demand value being determined at least in part
by reference to a torque demand signal received by the controller,
comprises the processor being configured to access the memory
device and execute the instructions stored therein.
[0026] In a further aspect of the invention for which protection is
sought there is provided a vehicle comprising a body, a plurality
of wheels, a powertrain to drive said wheels, a braking system to
brake said wheels, and a controller according to any preceding
aspect.
[0027] In an aspect of the invention for which protection is sought
there is provided a method of controlling by means of an electric
controller a motor vehicle powertrain, the method comprising
controlling the amount of torque generated by each of a plurality
of drive torque sources, each drive torque source being coupled via
a respective torque transfer arrangement to a respective group of
one or more wheels, [0028] the method comprising causing a first of
the drive torque sources, during acceleration, deceleration and
substantially constant speed operation, substantially continually
to apply a drive torque to a first group of one or more wheels to
which the first drive torque source is coupled acting in a first
direction relative to a longitudinal axis of the vehicle and
causing a second of the drive torque sources, during acceleration,
deceleration and substantially constant speed operation,
substantially continually to apply a drive torque to a second group
of one or more wheels to which the second drive torque source is
coupled, the direction of drive torque applied to the second group
being in a second direction opposite the first such that a net
drive torque applied to the first and second group in combination
corresponds substantially to a predetermined drive torque demand
value, the predetermined torque demand value being determined at
least in part by reference to a torque demand signal received by
the controller.
[0029] In one aspect of the invention for which protection is
sought there is provided a non-transitory computer readable carrier
medium carrying computer readable code for controlling a vehicle to
carry out the method of any preceding aspect.
[0030] In an aspect of the invention for which protection is sought
there is provided a computer program product executable on a
processor so as to implement the method of any preceding
aspect.
[0031] In a further aspect of the invention for which protection is
sought there is provided a computer readable medium loaded with the
computer program product of a preceding aspect.
[0032] In an aspect of the invention for which protection is sought
there is provided a processor arranged to implement the method of
any preceding aspect, or the computer program product of a
preceding aspect.
[0033] Within the scope of this application it is expressly
intended that the various aspects, embodiments, examples and
alternatives set out in the preceding paragraphs, in the claims
and/or in the following description and drawings, and in particular
the individual features thereof, may be taken independently or in
any combination. That is, all embodiments and/or features of any
embodiment can be combined in any way and/or combination, unless
such features are incompatible. The applicant reserves the right to
change any originally filed claim or file any new claim
accordingly, including the right to amend any originally filed
claim to depend from and/or incorporate any feature of any other
claim although not originally claimed in that manner.
[0034] For the avoidance of doubt, it is to be understood that
features described with respect to one aspect of the invention may
be included within any other aspect of the invention, alone or in
appropriate combination with one or more other features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] One or more embodiments of the invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0036] FIG. 1 is a schematic illustration of a vehicle according to
an embodiment of the present invention having a first torque
generator for driving front wheels of the vehicle and a second
torque generator for driving rear wheels of the vehicle; and
[0037] FIG. 2 is a plot of the amount of torque delivered by each
of first and second torque generators of the vehicle of the
embodiment of FIG. 1.
DETAILED DESCRIPTION
[0038] FIG. 1 is a schematic illustration of a vehicle 100
according to an embodiment of the present invention. The vehicle
100 has a powertrain 110 having first and second electric machines
121, 122 each operable as a propulsion motor (generating positive
drive torque in the direction of rotation of the electric machine)
or as a generator (generating electrical charge by applying
negative drive torque, being drive torque in a direction that is
against the actual direction of rotation of the electric machine).
The first electric machine 121 is arranged to drive a pair of front
wheels 135 of the vehicle via a first torque transfer arrangement
of the powertrain 110 that has a front differential gearbox 131 and
a pair of front half shafts 133. The second electric machine 122 is
arranged to drive a pair of rear wheels 145 of the vehicle via a
second torque transfer arrangement of the powertrain 110 that has a
rear differential gearbox 141 and a pair of rear half shafts 143.
The electric machines 121, 122 may be powered so as to act as
propulsion motors by means of a battery pack 150 via an inverter
160. The inverter 160 converts a supply of direct current (DC) from
the battery pack 150 to an alternating current (AC) supply to drive
the electric machines 121, 122 when required. When either or both
of the electric machines 121, 122 are operated as electric
generators, the inverter 160 converts AC current generated by the
electric machines 121, 122 to DC current to charge the battery
150.
[0039] A powertrain controller 110C is connected to the inverter
160 and controls operation of the electric machines via the
inverter 160. In particular, the powertrain controller 110C
controls the amount and direction of torque generated by the motors
121, 122. The powertrain controller 110C is also in communication
with an accelerator pedal module 111A having a driver operated
accelerator pedal 111AP and a brake pedal module 111B having a
driver operated brake pedal 111 BP. The powertrain controller 110C
receives electrical signals indicative of the position of the
accelerator and brake pedals 111AP, 111BP from the respective
modules 111A, 111 B with respect to an allowable range of travel of
the respective pedals 111AP, 111 BP. In some alternative
embodiments the brake pedal module 111B may be configured to
measure pressure applied to the brake pedal 111BP rather than
travel or displacement. However it is to be understood that, where
displacement or travel is measured, the signal indicative of travel
may be indicative of the amount of pressure applied. This is
because the amount of travel may be dependent on pressure applied,
as in the present embodiment, since the accelerator and brake
pedals 111AP, 111BP are configured to act against resilient
elements such as helical spring elements that oppose movement of
the respective pedal 111AP, 111BP with a force that increases with
increasing travel.
[0040] The powertrain controller 110C is configured to control the
electric machines 121, 122 to deliver a total combined amount of
drive torque to the wheels 135, 145 that is substantially equal to
that demanded by a driver by means of the accelerator pedal 111AP.
The powertrain controller 110C is also configured to simulate
compression braking normally exhibited by vehicles driven by
combustion engines. Thus, when a driver releases the accelerator
pedal 111AP the powertrain controller 110C may cause one or both of
the electric machines to deliver negative drive torque to the
associated wheels to simulate compression braking by effecting
regenerative braking. It is to be understood that in some
embodiments the amount of brake force that the electric machines
121, 122 are capable of generating may exceed that which an engine
may be capable of by compression braking, enabling a not
insubstantial amount of energy to be recovered by regenerative
braking.
[0041] The vehicle 100 also has a brake controller 115C that is
configured to control a foundation braking system 115B that is both
mechanically and electrically coupled to the brake pedal module
111B, and electrically coupled to the powertrain controller 110C.
The brake controller 115C is configured to cause the powertrain
controller 110C to effect regenerative braking in response to
actuation of the brake pedal 111 BP. If the powertrain controller
110C is unable to provide sufficient brake force by causing the
first and second electric machines 121, 122 to operate as
generators, or is unable sufficiently quickly to generate a
required brake force by regenerative braking alone whilst
mitigating the effects of backlash by reducing or limiting the rate
of change of drive torque as described herein, the brake controller
115C causes the foundation braking system 115B to apply friction
braking to the front and/or rear wheels 135, 145 of the vehicle
100.
[0042] In use, with the vehicle 100 substantially stationary and
prior to commencing motion over a surface, the powertrain
controller 110C is configured to cause the first electric machine
121 to develop positive drive torque in a reverse direction of
travel and the second electric machine 122 to develop positive
drive torque in a forward direction of travel. This configuration
causes the first and second torque transfer arrangements to be
placed in a condition of static torque loading in opposite senses.
In the static torque loading condition drive gears forming part of
the torque transfer arrangements become meshed in the respective
directions of torque loading. This condition is assumed by the
powertrain 110 under the control of the powertrain controller 110C
when a forward or reverse drive mode of vehicle operation is
selected by means of a forward/reverse driving mode selector 110S.
The selector is switchable between a park mode P, a reverse driving
mode D and a forward driving mode D. The powertrain controller 110C
permits a transition between modes when the vehicle 100 is held
stationary with the accelerator pedal 111AP undepressed (i.e. in a
released condition) and the brake pedal 111BP applied sufficiently
to maintain the vehicle 100 stationary.
[0043] If the park mode P is selected, the powertrain controller
110C causes substantially no torque to be developed by either of
the first and second electric machines 121, 122.
[0044] As noted above, if the forward drive mode D is selected, the
powertrain controller 110C causes the first electric machine 121 to
develop positive drive torque in a reverse direction, opposing
forward movement of the vehicle 100, whilst the second electric
machine 122 is caused to develop positive drive torque in a forward
direction of travel of the vehicle 100. In the forward drive mode
D, the powertrain controller 110C is configured to cause the amount
of torque developed in the forward direction to exceed that in the
reverse direction by a sufficient amount to enable the vehicle 100
to achieve a desired forward creep speed when on a surface of
sufficiently high surface coefficient of friction, `surface mu`,
and both the accelerator and brake pedals 111AP, 111BP
released.
[0045] If the reverse drive mode R is selected, the powertrain
controller 110C again causes the first electric machine 121 to
develop positive drive torque in the reverse direction, opposing
forward movement of the vehicle 100, and the second electric
machine 122 to develop positive drive torque in the forward
direction of travel of the vehicle 100, in a similar manner to that
when the forward drive mode D is selected, except that the net
torque on the vehicle is arranged to be in the reverse direction
and not the forward direction.
[0046] When motion of the vehicle 100 in the forward direction is
required, the driver selects the forward drive mode (with the brake
pedal 111 BP depressed) and releases the brake pedal 111BP. If the
accelerator pedal 111AP is then depressed, the powertrain
controller 110C causes a decrease in the amount of negative drive
torque generated by the first electric machine 121 and an increase
in the amount of positive drive torque generated by the second
electric machine 122. The first electric machine 121 is operated as
a generator, exerting negative drive torque on the front wheels
135. The first electric machine 121 causes regenerative braking to
occur at the front wheels 135 as the vehicle 100 moves over the
driving surface.
[0047] When it is required to slow the vehicle, the amount of
negative torque applied by the first electric machine 121 may be
increased and the amount of positive torque applied by the second
electric machine 122 may be decreased, but maintained in a positive
condition, acting against the negative torque applied by the first
electric machine 121. This enables repeated backlash crossing of
gears of the torque transfer arrangements associated with each
electric machine 121, 122 to be avoided.
[0048] It is to be understood that the work done by the first
electric machine 121 against the regenerative braking force applied
by the second electric machine 122 may be at least partially
recovered by the electrical energy generated by the second electric
machine 121 whilst applying negative torque.
[0049] Importantly, by maintaining the first electric machine 121
and first torque transfer arrangement in a negative torque
condition and the second electric machine 122 and second torque
transfer arrangement in a positive torque condition during
acceleration and deceleration of the vehicle, backlash of gears of
the first and second torque transfer arrangements may be avoided,
reducing noise, vibration and harshness (NVH) associated with
vehicle operation. This may be particularly beneficial when
executing a manoeuvre requiring repeated changes of direction of
movement of the vehicle 100 in rapid succession such as when
parking, which would otherwise result in repeated backlash of
gears.
[0050] It is to be understood that application of positive torque
to the rear wheels 145 (with respect to a forward direction of
travel) and negative torque to the front wheels 135 (with respect
to a forward direction of travel) rather than negative torque to
the rear wheels 145 and positive torque to the front wheels 135 may
be particularly advantageous because the weight transfer associated
with acceleration and deceleration in the forward or reverse
direction acts to increase the proportion of the weight of the
vehicle 100 borne by the wheels that are developing forces to cause
the acceleration or deceleration.
[0051] It is to be understood that, in the event that a relatively
high rate of deceleration is demanded by a driver, for example by
heavy pressing on the brake pedal 111BP in an emergency braking
scenario, the first electric machine 121 and in addition the second
electric machine 122 may be employed to deliver regenerative
braking and/or a friction-based foundation braking system may be
employed to supplement the regenerative braking developed by one or
both of the electric machines 121, 122.
[0052] In some embodiments, when the vehicle 100 is in the forward
drive mode D or reverse drive mode R, the first electric machine
121 is configured to generate only torque acting in the direction
of reverse travel of the vehicle 100 and the second electric
machine 122 is configured to generate only torque acting in the
direction of forward travel of the vehicle 100.
[0053] In the present embodiment, the powertrain controller 110C is
configured wherein, when the amount of driver demanded torque in
the forward direction of driving approaches a threshold value from
a value below the threshold value, in the present embodiment a
value that is approaching the positive drive torque limit of the
second electric machine 122, the first electric machine 121 is
controlled to transition from a negative torque application
condition to a positive torque application condition. The
transition from the negative torque application condition to the
positive torque application condition is controlled so that, as the
amount of torque passes through zero, the rate of change of the
amount of torque developed by the first electric machine 121 is
reduced to a value not exceeding a predetermined torque rate limit
value. This reduces the amount of NVH developed by the first torque
transfer arrangement as gears of the first torque transfer
arrangement experience a reversal of the direction of torque
loading to which they are subject.
[0054] Once the torque reversal has taken place, the limit on the
maximum allowable rate of change of torque developed by the first
electric machine 121 is lifted. The first electric machine 121 is
then controlled by the controller 110C, in combination with the
second electric machine 122, in order to meet driver torque
demand.
[0055] An example of the manner in which the powertrain controller
110C is configured to operate in the present embodiment is
illustrated graphically in FIG. 2. Other configurations may be
useful in some embodiments.
[0056] Trace P1 of FIG. 2 shows the amount of net torque generated
by the first electric machine 121, trace P2 shows the amount of net
torque generated by the second electric machine 122 and trace P3
shows the total amount of net torque generated by the first and
second electric machines 121, 122 in combination.
[0057] Prior to time t0 the vehicle 100 is substantially stationary
on substantially level ground with brake pedal 111 BP depressed.
Since the vehicle 100 is stationary, depression of the brake pedal
111BP causes the friction-based foundation braking system 115B to
apply brake pressure at the front and rear wheels 135, 145.
[0058] When the vehicle 100 is held stationary by means of the
brake pedal 111BP and the forward driving mode D is selected by
means of driving mode selector 110S then, as described above,
powertrain controller 110C causes the first and second electric
machines 121, 122 to apply similar amounts of drive torque to the
front and rear wheels 135, 145, respectively, but in opposite
senses such that the second electric machine 122 acts to drive the
vehicle 100 in a forward direction whilst the first electric
machine 121 acts to drive the vehicle 100 in a reverse direction
opposite the forward direction. The amounts of torque generated by
the first and second electric machines 121, 122 are arranged such
that a net positive amount of drive force acts on the vehicle 100
in a forward direction if the forward drive mode D of the vehicle
100 is selected, this torque being opposed by the braking system
115B under the control of brake controller 115C due to depression
of the brake pedal 111BP. In the present embodiment the first
electric machine 121 causes a combined torque TQ1 of around -100 Nm
to be applied to the front wheels 135 (the combined applied torque
being substantially -100 Nm between the wheels, i.e. an average
torque of -50 Nm per front wheel 135) whilst the second electric
machine 122 causes a combined torque of TQ2 of around 500 Nm to be
applied by the rear wheels 145 (the combined applied torque being
substantially 500 Nm between the wheels, i.e. an average torque of
250 Nm per rear wheel 145). A net torque of 300 Nm is therefore
applied to the wheels by the first and second electric machines
121, 122.
[0059] At time t0 the driver releases the brake pedal 111 BP. Upon
release of the brake pedal 111BP the friction braking system 115B
is released under the control of the brake controller 115C. Since a
net torque in a forward direction of vehicle travel exists, the
vehicle 100 begins to accelerate in a forward direction provided
the net torque is sufficient to overcome frictional and any other
resistance to movement.
[0060] It is to be understood that if the vehicle 100 is held
stationary by the braking system 115B in the reverse drive mode R,
the powertrain controller 110C is configured in the present
embodiment to cause the first electric machine to exert a torque in
a reverse direction (negative torque) on the front wheels 135
totalling substantially 500 Nm (250 Nm per wheel) and the second
electric machine 122 to exert a torque in a forward direction on
the rear wheels 145 totalling substantially 100 Nm (50 Nm per
wheel) such that a net torque on the vehicle 100 due to the
electric machines 121, 122 acts in the reverse direction, i.e. the
direction of intended movement when in the reverse drive mode R.
Thus, selection of the forward drive mode D results in the
application of torque by the first and second electric machines
121, 122 in the same direction as in the case the reverse drive
mode R is selected, the relative amounts of torque differing
according to whether the forward drive mode D or reverse drive mode
R is selected.
[0061] In some alternative embodiments, instead of a net positive
torque being caused to be applied by the powertrain controller 110C
in the forward direction when the vehicle is stationary in the
forward drive mode D, and a net positive torque in the reverse
direction when the vehicle is stationary in the reverse drive mode
R, the powertrain controller 110C may be configured to cause a net
torque of substantially zero to be applied under similar
conditions. Other arrangements may be useful.
[0062] At time t1 in the example of FIG. 2 the driver depresses the
accelerator pedal 111AP. The powertrain controller 110C responds by
causing the amount of positive drive torque developed by the second
electric machine 122 to start to increase.
[0063] At time t2 the second electric machine 122 is developing
approximately 50% of its maximum allowable continuous torque, TQ6
and the driver is still demanding an increase in drive torque. The
controller 110C causes the amount of torque generated by the second
electric machine 122 to stop increasing and, substantially
simultaneously, begins to reduce the amount of negative torque
generated by the first electric machine 121.
[0064] The controller 110C causes the amount of negative torque
developed by the first electric machine 121 to decrease at a rate
that is determined according to the amount of torque demanded by
the driver, as determined by the powertrain controller 110C in
dependence on accelerator pedal position and vehicle speed. In the
present embodiment, the powertrain controller 110C implements a
torque filter that may be referred to as a `drivability filter`. A
`raw` value of driver torque demand based on accelerator pedal
position and vehicle speed is input to the filter, which outputs a
smoothed driver torque demand value. The controller 110C controls
the first and second electric machines 121, 122 to deliver a net
torque averaged over the wheels of the vehicle that is
substantially equal to the smoothed driver torque demand value. The
purpose of the filter is to smooth driver torque demand such that
the net rate of change torque averaged over each driven wheel does
not become excessively large if a driver rapidly depresses or
releases the accelerator pedal 111AP.
[0065] When the amount of torque developed by the first electric
machine 121 reaches a predetermined value, -TQ3, of around -10 Nm,
at time t3, the powertrain controller 110C causes a decrease in the
rate of change of torque developed by the first electric machine
121 so that the rate does not exceed a predetermined torque
reversal rate limit. It is to be understood that no decrease in
rate of change of torque will be required if the rate of change is
already less than or equal to the predetermined torque reversal
rate limit. Substantially simultaneously, the controller 110C
causes the amount of torque developed by the second electric
machine 122 to increase at a rate such that the net torque applied
by the first and second electric machines 121, 122 meets the
prevailing driver torque demand (post drivability filter), i.e.
such that the net rate of change of torque averaged over each
driven wheel of the vehicle 100 meets the predetermined (smoothed)
driver torque demand. The transition between different electric
machines 121, 122 causing the increase in net drive torque is
arranged to be substantially seamless, such that any increase in
NVH associated with the transition is negligible.
[0066] In the present embodiment, the predetermined torque reversal
rate limit is a substantially constant value under all driving
conditions and is determined empirically to be a value that results
in relatively little or no NVH being perceived by a user when the
amount of torque applied by the first electric machine 121
undergoes torque reversal at time t4. In the present embodiment the
predetermined torque reversal rate limit is around 3-20 Nm per
second although other values may be useful in some embodiments.
Thus, the torque may transition from -10 Nm to +10 Nm in around 1s
in some embodiments.
[0067] The predetermined torque reversal rate limit may in some
alternative embodiments be dependent on vehicle speed and/or
accelerator pedal position. For example in some embodiments the
predetermined torque reversal rate limit may increase with vehicle
speed, since it may be determined that a vehicle occupant is less
sensitive to NVH associated with torque reversal at higher vehicle
speeds due for example at least in part to masking of the NVH
associated with torque reversal by additional sources of NVH such
as NVH associated with tyres of the vehicle and/or airflow over the
vehicle. In addition or instead, the predetermined torque reversal
rate limit may be arranged to increase with increasing driver
torque demand since a driver may be willing to tolerate higher
levels of NVH associated with torque reversal when demanding higher
acceleration rates, for example when performing an overtaking
manoeuvre.
[0068] Once the torque reversal has taken place, at time t5 the
powertrain controller 110C determines that the amount of driver
torque demand is continuing to increase. The controller 110C halts
further increase in the amount of torque generated by the second
electric machine 122 and causes the amount of torque generated by
the first electric machine 121 to increase according to the rate of
increase of driver torque demand. At time t6 the amount of torque
developed by the first electric machine 121 reaches its maximum
allowable continuous value TQ5. Accordingly, at time t6 the
controller 110C causes the second electric machine 122 to increase
the amount of torque generated thereby, until at time t7 the driver
torque demand no longer increases, and remains substantially
constant. At time t7, the first electric machine 121 is developing
a substantially continuous torque of value TQ5 whilst the second
electric machine 122 is developing a substantially continuous
torque of value TQ8, resulting in a total net torque applied across
the four wheels 135, 145 of value TQ9.
[0069] As described above, embodiments of the present invention
have the advantage that, in vehicles having independent drive
torque sources coupled to respective different groups of one or
more wheels via a respective geared torque transfer arrangement, an
amount of NVH experienced by a vehicle occupant when a reversal in
the direction of torque applied to a torque transfer arrangement
takes place may be reduced, optionally to a substantially
imperceptible level, optionally substantially to zero, whilst
vehicle response to driver torque demand remains substantially
unaffected. Some embodiments of the invention have the advantage
that substantially no torque reversal need take place when driver
demanded torque is below a certain value since the propulsion
source driving one group of one or more wheels may continue to
provide positive drive torque whilst the propulsion source driving
another group of one or more wheels provides negative torque. The
powertrain controller 110C may adjust the amount of positive drive
torque provided by the propulsion source that continues to provide
positive drive torque, and optionally the amount of negative drive
torque provided by the other propulsion source, in order that the
total torque delivered by the propulsion sources 121, 122 continues
to meet the amount demanded by the driver. It is to be understood
that the amount of torque demanded by the driver may be
substantially constant, or increasing or decreasing. Nevertheless,
the powertrain controller 110C may control the propulsion sources
such that driver torque demand is met substantially seamlessly.
[0070] It is to be understood that torque reversal operations may
take placed during periods of acceleration or deceleration of a
vehicle. In some embodiments torque reversal operations may be
caused to take place under certain conditions when the amount of
driver demanded torque is substantially constant, in order to
prepare the vehicle for subsequent acceleration or deceleration
events before driver torque demand increases or decreases.
[0071] For example, in some embodiments, if (say) the first and
second electric machines 121, 122 are both delivering positive
drive torque and the amount of driver demanded torque reduces to a
sufficiently low (but positive) value, the powertrain controller
110C may cause the first electric machine 121 to transition from
delivering positive drive torque to delivering negative drive
torque whilst the second electric machine 122 continues to deliver
positive drive torque. This is at least in part in anticipation of
the possibility that regenerative braking may be required if the
driver reduces the amount of demanded torque further.
[0072] Thus, the controller 110C may anticipate a future increase
or decrease in torque demand, and prepare the powertrain
accordingly. In some embodiments the controller 110C may be
configured to receive data indicative of the gradient of terrain
ahead of the vehicle. In the event the gradient is positive, i.e.
inclined upwardly, the controller 110C may prepare the powertrain
for an increase in torque demand and ensure that both electric
machines 121, 122 are developing positive drive torque. In the
event the gradient is negative, i.e. inclined downwardly, the
controller 110C may prepare the powertrain for a decrease in torque
demand, and a scenario in which the powertrain may be required to
develop negative drive torque, i.e. develop a net torque in a
direction opposite the direction of travel. Accordingly, in such a
situation, if both electric machines 121, 122 are developing
positive drive torque the controller 110C may cause at least one of
the electric machines, such as the first electric machine 121, to
transition to delivering negative drive torque, i.e. positive drive
torque in the reverse direction opposite the forward direction of
travel. The second electric machine may be controlled to deliver an
additional amount of positive (forward) drive torque so that the
net drive torque remains substantially unchanged. As a consequence,
the first torque transfer arrangement associated with the first
electric machine 121 undergoes a lash crossing in which the
direction of torque transfer reverses direction such that, if a
relatively rapid increase in negative drive torque is subsequently
required, to implement regenerative braking, relatively harsh NVH
associated with torque reversal in response to accelerator pedal
lift off or brake pedal depression is avoided.
[0073] The powertrain controller 110C reduces the rate of change of
torque generated by the first electric machine 122 as the torque
generated by the first electric machine 121 reverses direction so
that the rate does not exceed the predetermined torque reversal
rate limit, reducing NVH associated with backlash of gears of the
first torque transfer arrangement. The amount of torque generated
by the second electric machine 122 is controlled so as to maintain
the driver demanded torque as the transition to negative torque
generation by the first electric machine 121 takes place.
[0074] If both the first and second electric machines 121, 122 are
delivering positive drive torque and the amount of driver demanded
torque reduces to a value sufficiently low to require both motors
121, 122 to provide regenerative braking, the powertrain controller
110C may cause one of the first and second electric machines 121,
122 to transition from delivering positive drive torque to
delivering negative drive torque and subsequently cause the other
of the first and second electric machines 121, 122 to transition
from delivering positive drive torque to delivering negative drive
torque. In both cases, the powertrain controller 110C attempts to
reduce the rate of change of torque generated by the respective
electric machine 121, 122 undergoing torque reversal as the torque
generated by the electric machine 121, 122 reverses direction, so
as to reduce NVH associated with backlash of gears of the
respective torque transfer arrangements. The amount of torque
generated by the electric machine 121, 122 not experiencing torque
reversal at that time is controlled so as to provide a desired
value of net torque at the wheels 135, 145 of the vehicle 100. Thus
the control of torque applied to the torque transfer arrangements
by the respective motors 121, 122 allows substantially seamless
transitions between positive and negative values of applied torque
and between negative and positive values of applied torque that are
substantially imperceptible to a driver. It is to be understood
that in some embodiments one electric machine 121, 122 may be
permitted to exceed one or more normal maximum steady state
performance parameter values for a relatively short period of time
whilst the other electric machine 122, 121 undergoes torque
reversal. Thus, for example, in some embodiments one electric
machine 121, 122 may be permitted transiently to deliver an amount
of torque exceeding the amount for which it is rated under steady
state conditions in order to compensate for a reduction in the
amount of torque delivered by the other 122, 121.
[0075] It is to be understood that, in some embodiments, an engine
may be provided in addition to the first and second electric
machines 121, 122. Thus the vehicle 100 may be a hybrid electric
vehicle in some embodiments. The hybrid vehicle may be a parallel
hybrid vehicle in which the engine is configured to deliver drive
torque to one or more wheels, or a series hybrid vehicle in which
the engine is configured to power a generator to generate
electrical power when required to charge the battery or drive one
or both of the electric machines 121, 122.
[0076] Embodiments of the present invention have the advantage that
NVH associated with powertrain gear backlash when a portion of the
powertrain undergoes torque reversal may be substantially
eliminated or at least reduced, optionally to a substantially
imperceptible level.
[0077] Throughout the description and claims of this specification,
the words "comprise" and "contain" and variations of the words, for
example "comprising" and "comprises", means "including but not
limited to", and is not intended to (and does not) exclude other
moieties, additives, components, integers or steps.
[0078] Throughout the description and claims of this specification,
the singular encompasses the plural unless the context otherwise
requires. In particular, where the indefinite article is used, the
specification is to be understood as contemplating plurality as
well as singularity, unless the context requires otherwise.
[0079] Features, integers, characteristics, compounds, chemical
moieties or groups described in conjunction with a particular
aspect, embodiment or example of the invention are to be understood
to be applicable to any other aspect, embodiment or example
described herein unless incompatible therewith.
* * * * *